1. Field of the Invention
The invention relates to a device in which a preprogrammed micromirror array redistributes the laser output beam energy to produce a desired two-dimensional machining pattern on a work piece.
2. Description of Related Art
It is known that in laser machining, particular importance is attached to both the quality of the beam produced by a laser and the shaping of that beam for the desired use. The laser output beam quality and shape determine the quality, quantity and efficiency of work piece machining. In many lasers, the output energy distribution over the beam profile is nonhomogeneous and if not reshaped to produce a uniform distribution would result in uneven machining over the work piece surface. Various approaches have been used to homogenize a laser beam profile to solve this problem.
One of the simplest devices to produce a homogenized beam profile is described by Fan et al. in U.S. Pat. No. 4,744,615 issued on May 17, 1988. In the Fan et al. patent, a coherent laser beam having non-uniform spatial intensity distributions is transformed by a multi-mirror tunnel in which the laser energy is reflected off the multiple mirrors such that there is a uniform energy profile at the exit of the tunnel.
U.S. Pat. No. 5,041,862, Rossman et al. xe2x80x9cLens Screenxe2x80x9d, issued on Aug. 20, 1991 discloses a two-dimensional optical lenslet array that divides the laser beam into beamlets, which are subsequently reimaged to overlap their individual beamlet profiles producing an homogenized beam profile. Similarly, reshaping and homogenization of a laser beam is conventionally performed by XMR cylindrical lens arrays like 2Z17-E0125 or monolithic lens arrays of crossed cylindrical lenses. The simplest set-up consists of an array of crossed cylindrical followed by a focusing lens. The rectangular lenslets of the array have a clear aperture of rectangular shape. Collimated light coming into the lens array will be divided by the lenslets into beamlets of a rectangular beam profile. Each beamlet is focused by the lens array and diverges after the focal plane. The convex lens refracts each beamlet so that it fills the focal of the optical axis.
In addition, the prior art also includes:
U.S. Pat. No. 5,864,430, Dickey et al entitled xe2x80x9cGaussian beam profile shaping apparatus, method therefor and evaluation thereofxe2x80x9d, issued on Jan. 26, 1999 discloses a method and apparatus for mapping a Gaussian beam into a beam with uniform irradiation profile by exploiting the Fourier transform properties of lenses.
U.S. Pat. No. 5,925,271 to Pollack, et al. and entitled, xe2x80x9cLaser beam shaping device and process including rotating mirrorxe2x80x9d, issued Jul. 20, 1999. discloses a system in which one stationary beam shaping mirror and at least one rotary mirror is used to achieve an elliptical beam on a surface.
German patent DE 19724060A1 describes an apparatus which creates a homogenized excimer laser beam by splitting the beam, inverting the profile and coaxial recombination of the inverted beam profile with the original profile. The practical implementation of this beam homogenizer is manufactured by Micro/Las GMBH.
The foregoing patents describe technology, which accomplish beam shaping with fixed and/or rotating optical components and are capable of changing beam profile shape by mechanically replacing or reorienting the optical components.
Homogenized laser beams are used for a variety of materials machining purposes including drilling, contouring surfaces, cutting, scribing, trimming and pattern depositions. Typically, Co2 lasers are used for scribing, drilling and machining. Excimer lasers are used for film ablation, flex circuits and relief cutting. YAG lasers are used for trimming resistors, capacitors, marking and cutting of metals, semiconductors and absorptive synthetics.
In the case of U.S. Pat. No. 5,676,866 to Baumen et al, an apparatus is disclosed that creates an array of beamlets, which are individually deflected on to a work piece to simultaneously drill holes at different points. A beam homogenizer is described, for example, in U.S. Pat. No. 5,041,862, Rossman et al. for the purpose of making certain that the array of machining beamlets all have the same intensity.
Laser beam machining with uniform beam profiles requires beam homogenization when the laser output beam energy profile is non-uniform. Further, changes in patterns for laser machining of a work piece is limited to changes/adjustments of optical components and or mechanical displacements of the work piece.
The prior art does not appear to disclose or suggest a suitable a method of laser beam homogenization and work piece shaping that has the ability to provide high speed, high resolution, and complex pattern laser beam machining of a work piece.
Briefly described, the invention combines the function of laser beam homogenization with shaping of the beam using a preprogrammed micromirror array device to produce a specified spatial energy distribution that can rapidly and accurately machine a work piece.
A preprogrammed thin film micromirror array (TMA) has individually addressable and moveable mirrors capable of redistributing the laser output beam energy to produce a desired two-dimensional machining pattern. Simple and complex predetermined energy patterns can be created and rapidly changed. Different patterns can be generated on successive laser energy pulses, both in energy distribution and geometric location, to create accurate, complex three-dimensional machining of a work piece, not easily achieved by conventional machining techniques. An electronic tracking system is included to precisely align the laser energy patterns with work piece features/indices.
A special application of the invention is laser beam homogenization, i.e. laser beam shaping, to produce a uniform spatial energy distribution from a laser with non-uniform energy distribution. The disclosed invention provides automatic, continuous adjustment of beam shaping to maintain homogenization in accordance with changes in laser beam output energy profile not available from fixed optical systems.
The invention is best understood from the following detailed description when read in connection with the accompanying drawings.